Sea Level Rise Impact on the Beach Zone of Katerini Region, NW Aegean Sea
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15th International Conference on Environmental Science and Technology Rhodes, Greece, 31 August to 2 September 2017 Sea level rise impact on the beach zone of Katerini region, NW Aegean Sea Tsanakas K.1, Poulos S.E.1 And Monioudi I.2 1Department of Geology & Geoenvironment, University of Athens, Laboratory of Physical Geography, Panepistimioupoli, Zografou, 15784, Athens 2Department of Marine Sciences, University of the Aegean, University Hill, Mytilene, Greece *corresponding author: Tsanakas K. e-mai: [email protected] Abstract: The present contribution provides an initial enhance the already beach erosion, with severe impacts on assessment of the impacts of the longterm (climatic, i.e. coastal activities, infrastructure and assets (Jiménez et al., sea level rise) and episodic (meteorological) on the sandy 2012), and the beach carrying capacity for beach zone along the coast of Katerini region (NW Aegean recreation/tourism (Valdemoro and Jiménez, 2006). Sea). Thus, the future retreat of the coastline, due to sea In the case of the Greece 1/3 of its coastline has been level rise (SLR) induced by climate change, has been subjected to erosion with the West Macedonia prefecture estimated on the basis of an ensemble of 5 coastal having its 45.1% under erosion to be second in order after morphodynamic models. Model’s outputs showed that Crete where erosion covers the 65.8% of its coastline shoreline retreat range between 7.9-27.3 m and 23.5-70.0m (EUROSION, 2004). Obviously, erosion affects primarily for SLR of 0.38m and 1.0m, respectively. An initial beaches, which accounts for the 36% of the Greek assessment of coastal flooding has been examined after coastline, and from which more than 30% have been under consideration of the astronomical tidal range, storm surge erosion (Alexandrakis et al., 2013). estimates and calculations of wave runup for intensive wave conditions (Ho>4 m). The results showed that the The present contribution provides an initial assessment of locations adjacent to Paralia and Olympiaki Akti the impacts of the longterm (sea level rise - SLR) and residences are the most vulnerable to coastal flooding, episodic (meteorogical) in the case of the sandy beach zone whilst in the case of future sea level the study area could along the coast of Katerini region. be subjected to coastal flooding. 2. Study area Keywords: coastline retreat, runup, storm surge, sea level The study area is located at the NW part of Thermaikos rise, coastal hazards Gulf (NW Aegean Sea) (Fig. 1). It accommodates a low lying coastal relief (slopes <1%) of uncosolidated alluvial sediments at the easternmost part of the extensive alluvial 1. Introduction plain of Katerini. The coastline of the area under Beaches (i.e. the low-lying coasts consisting of investigation is oriented in a NNE-SSW direction and has a unconsolidated sediment) form extremely important total length of up to 21 km. It receives the sediments of 6 economic resources, particularly for Greece (Velegrakis et intermittent flow torrents which drain an area of >625 km2, al., 2005), the significance of which in the present which in combination with the prevailing marine processes financial climate has a distinctive role for the Greek (e.g. longshore sediment transport), control the overall economy. Beaches are also very dynamic coastal morphology of the coastal zone. The latter incorporates the environments and are currently under increasing erosion Alykes lagoon at its northern part, a significant salt (EUROSION, 2004), which can be differentiated into: (i) production unit in Greece with a major ecological long-term erosion, i.e. irreversible retreat of the shoreline footprint. Furthermore, Paralia Katerinis settlement, position, due to mean sea level rise and/or negative coastal located at the central part of the study area, is an important sedimentary budgets (Dan et al., 2009) that force beach touristic unit with considerable contribution to the local landward migration and/or drowning; and (ii) short-term economy. erosion, caused by storm waves/surges, which may or may Waves related to SE winds are considered to be the most not result in permanent shoreline retreats (List et al., important in terms of magnitude (Ho>4 m). The study area 2006), but can nevertheless be devastating (Smith and is a microtidal marine environment exposed to a mean tidal Katz, 2012). Climate change, either as mean sea level rise range of about <20 cm (Hellenic Navy Hydrographic (a moderate estimate of 0,4m for 2100 after IPCC, 2013) Service, 2005). and/ episodic storm events will both initiate and/or CEST2017_01282 Figure 1. Study area location map depicting also S1-S7 cross-shore profiles. 3. Data and methods A full description of the aforementioned models The coastal retreat due to sea level rise has been assessed (morphodynamic concept and equations) are presented by through the application of an ensemble of three analytical Monioudi et al (2016). (Edelman, 1972; Bruun, 1988; Dean, 1991) and two The models were applied at seven -shore-normal profiles numerical models (Larson and Kraus (S beach), 1989; for high wave conditions related to SE direction, i.e. wave Leont’yev, 1996). height (Ho) of 5.5 m and period (T) 9.0 s and two SLR The Bruun model (e.g. Bruun, 1988) is based upon the senarios 0.38 m (IPCC, 2013) and 1 m (e.g. Pfeffer et al., concept of the equilibrium profile (Zhang et al., 2004), 2008). Morphometric measurements along seven shore- with the coastal retreat controlled by the height of the normal profiles (for locations, see Fig.1) were carried out beachface and the distance between the coastline and the by means of a Nikon A20 Total Station for the subaerial closure depth (Komar, 1998). Edelman’s (1972) model parts and a Hondex single-beam portable echo sounder for can deal with more realistic beach profiles and temporally- the subaqueous parts. variable sea level changes. The Dean (1991) model, A gross estimate of potential coastal flooding (storm developed initially for the diagnosis/prediction of storm- induced) could be approached by calculating the total driven coastal retreat, is also based on the equilibrium water level (TWL) as the sum: Tidal range (T) + storm profile concept, with the coastal retreat controlled by the surge (SS) + Wave runup (R2%) + Sea-level rise (SLR) water depth at wave breaking, the height of breaking In the case of the Thermaikos Gulf (NW Aegean Sea) tidal waves, the surf zone width and the beach sediment texture. amplitude is in the order of 0.1 m, the storm surge accounts The S-Beach model (Larson και Κraus, 1989) is a ‘bottom- for 0,4 ±),1 m (after Karambas (2015) and Androulidakis up’ morphodynamic model, consisting of combined et al (2015)) whilst SLR = 0 for present time becoming hydrodynamic and sediment transport modules and 0,38 m at 2100 (according to moderate scenario of IPCC containing detailed descriptions of the wave transformation (2013). and sediment transport in the coastal zone. The sediment continuity equation is addressed by finite differences and a The wave runup could be approached using the following ‘stair – step’ beach profile discretisation, whereas sediment equations provided by Stockton et al. (2006), Komar 1998 transport is controlled by the wave energy flux and the and Holman (1986); these are: 0.5 beach slope. Finally, the model based on the Leont’yev L (0.563 2 0.004) (1996) algorithm uses the energetics approach (Battjes and R 1.10.35(H L ) 2% o o 2 Janssen, 1978), with the wave energy balance in the cross- shore direction controlled by the wave propagation angle, 0.5 0.5 R2%=0.36*g *β*H0 *T0 the wave energy and its dissipation; sediment transport b rates are predicted separately for the surf and swash zones. R2% = Ηmo α ξο +c CEST2017_01282 where, Ho: offshore wave height, To: wave period, β study area. On the contrary, the highest values of beach foreshore slope that in the case of the Greek tideless retreat, have been attributed to beach profile S5 that is environment coincides to some extend with beach face, located adjacent to Paralia Katerinis residence area with 0.5 ξο=β/(Hο/Lο) whilst according to Hunt’s (1959) data major economic impacts on the tourism sector and the suggested α=1 b=1 and c=0 for deep water regular waves. local economy in general. 4. Results and Discussion On the basis of these estimates the current beach widths The estimated values of beach retreat, for the seven will be reduced by at least 30% (S6) and up to 63% (S2) for the moderate scenario of SLR, with the exception of S3 locations S1-S7, their averages and for comparison, the current beach widths are presented on Table 1. location where retreat is almost equal to beach width. If SLR reaches the 1 m, then there will be a total loss of the Beach retreat ranges from 7.9m to 27.3m for SLR=0.38m beach width, only with the exception of S6 where the beach and from 23.5m up to 70m for SLR=1.0m. The smallest will be reduced by 80%. retreat values for both scenarios of SLR have been calculated for the S7 beach profile, which is located at the mouth of Mavroneri torrent at the southernmost part of the Table 1. Beach retreat in (m) for each cross-shore profile for SLR 0.38m and 1.0m until 2100. Beach SLR Beach Beach retreat (m) Profile width (m) loss (%) Leont'yev SBEACH Edelman Bruun Dean Average 0.38 4.0 3.4 13.1 16.3 21.1 11.6 50.4 S1 23 1 18.2 18.2 34.4 43.0 42.5 31.3 >100 0.38 3.0 3.2 15.0 14.1 24.2 11.9 62.6 S2 19 1 7.8 7.5 39.6 37.2 48.8 28.2 >100 0.38 2.7 2.8 18.1 15.6 29.3 13.7 98.0 S3 14 1 14.5 14.3 47.8 41.1 58.9 35.3 >100 0.38 2.9 3.08 17.9 18.1 28.8 14.1 >100 S4 10 1 12,0 12.6 47.1 47.7 58.1 35.6 >100 0.38 32.6 34.8 17.2 23.8 27.8 27.3 43.3 S5 63 1 92.1 93.9 45.4 62.7 56.0 70.0 >100 0.38 3.1 3.4 14.3 14.2 23.0 11.4 29.7 S6 39 1 17.8 16.9 37.6 37.4 46.3 31.5 80.0 0.38 2.6 2.4 9.2 10.1 14.9 7.9 52.6 S7 15 1 17.8 18.3 24.4 26.8 30.1 23.5 >100 Table 2.